He's not my bf - what are we?

Both of us are very busy and don't often have time to go out. Our first date went remarkably well (moonlight beach) and later at work we let each other know how we feel. Our next date is soon at a coffee shop - to discuss our plans for a future date up to Los Angeles this summer. So we've only been on one date so far, but we see each other at work about every day and he writes me letters. It's not often we get to be alone together but we both really like each other. We haven't donee anything yet but I know he wants to as do I.